%%
%% The LaTeX Companion, 3ed
%%
%% Example A-3-21 on page II-670 in "Manipulating boxed material".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{111.0pt}
%StartShownPreambleCommands
\usepackage{calc}
\newsavebox{\fcolbox} \newlength{\fcolwidth}
\newenvironment{fcolumn}[1][\linewidth]
  {\setlength{\fcolwidth}{#1-2\fboxsep-2\fboxrule}%
   \begin{lrbox}{\fcolbox}\begin{minipage}{\fcolwidth}}
  {\end{minipage}\end{lrbox}\noindent\fbox{\usebox{\fcolbox}}}
%StopShownPreambleCommands

\begin{document}
\begin{fcolumn}   In this environment verbatim text like
  \verb=\fcolbox= can be used.                  \end{fcolumn}
\end{document}
